GM9.12

The inherent links between tectonics, surface processes and climatic variations have long since been recognised as the main drivers for the evolution of orogens. Oceanic and continental subduction and collision processes lead to distinct topographic signals. Simultaneously, different climatic forcing factors and denudation rates substantially modify the style of deformation leading to different stress and thermal fields, strain localisation and even deep mantle evolution. An ideal area where the above-mentioned processes and their connections can be studied is the India-Eurasia collision zone.

Understanding the complex interplay between tectonics, erosion, sediment transportation and deposition requires the coupled application of thermo-mechanical and surface processes modelling techniques. To this aim, we used a 3D coupled numerical modelling approach. The influence of different plate convergence, erosion and sedimentation rates has been tested by the thermo-mechanical code I3ELVIS (Gerya and Yuen, 2007) coupled to the diffusion-advection based (FDSPM) surface processes model.

We show preliminary results to demonstrate  that the diffusion-advection erosion implementation has significant effects on local and regional mass redistribution and topographic evolution within narrow, curved, high orogens such as the Himalayas and their syntaxes, where erosion is a dominant forcing factor. We also discuss possible implications from different erosion/sedimentation implementations such as DAC (Ueda et al., 2015; Goren et al., 2014) in combination with the reference thermo-mechanical model to analyse changes in orogenic development as a consequence of different erosional processes in more detail.

References:

Gerya, T. V., & Yuen, D. A. (2007). Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Physics of the Earth and Planetary Interiors, 163(1-4), 83-105.
Ueda, K., Willett, S. D., Gerya, T., & Ruh, J. (2015). Geomorphological–thermo-mechanical modeling: Application to orogenic wedge dynamics. Tectonophysics, 659, 12-30.
Goren, L., Willett, S. D., Herman, F., & Braun, J. (2014). Coupled numerical–analytical approach to landscape evolution modeling. Earth Surface Processes and Landforms, 39(4), 522-545.

How to cite: van Agtmaal, L., Balazs, A., May, D., and Gerya, T.: Surface processes control on orogenic evolution: inferences from 3D coupled numerical models and observations from the India-Eurasia collision zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8243, https://doi.org/10.5194/egusphere-egu21-8243, 2021.

Paleoaltimetry is a powerful tool to study tectonic, climate and surface processes interactions. Indeed, stable isotope composition of meteoric water can be correlated with the elevation of reliefs. The δ18O and δD of orogenic rainfall decrease while the elevation increase. Current paleoaltimetric methods based on stable isotope, including the study of pedogenic carbonates and micas associated with fault or shear zones, represent an indirect way to obtain stable isotope « paleometeoric fluid » composition. These methods do not provide simultaneously the δ18O and δD values implying the use of isotope exchange equation, source of signficant errors (up to +/- 1000m).

We have developed a new method which allow to directly acces at both the δ18O and δD of « paleometeoric » fluids with a good precision and margin of error less than +/- 200m . This method has been developed on the stable isotope composition of fluid inclusion trapped in quartz veins. The developed experimental protocol allows to extract small quantity of fluid (~10mL) and directly analyse both the δ18O and δD with a OA-ICOS Spectroscopy. Tested on 18 Miocene alpine quartz veins from the Mont-Blanc and the Chenaillet massifs the stable isotope composition of the fluids fit very well with meteoric isotopic signature and highlight the robustness of stable isotope ratio through geological time.

More over, our results indicate that Miocene precipitation was way more positive (-4,8 to -9 ‰ for δ18O and -38,2 to 68,8‰ for δD) in the Mont-Blanc massif area than modern precipitation (-12,9 to -18 ‰ for δ18O and -101,1 to -144,25‰ for δD) which indicate that the massif was still at low elevation at this time. In contrast the « paleoprecipitation » of the Chenaillet massif fall in the same range than modern precipitation (-83 to -120,3 ‰ for δD and -11,8 to -16,9 ‰ for δ18O) which indicate this massif has already reached his present altitude (~ 2500m).

How to cite: Melis, R., Gardien, V., Mahéo, G., Lécuyer, C., Leloup, P.-H., Jame, P., and Bonjour, E.: Stable isotope composition of fluid inclusions in quartz minerals : New method for paleoaltimetry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15983, https://doi.org/10.5194/egusphere-egu21-15983, 2021.

Resolving the thermal history of sedimentary basins through geological time is essential when evaluating the maturity of source rocks within petroleum systems. Traditional methods used to estimate maximum burial temperatures in prospective sedimentary basin such as and vitrinite reflectance (%Ro) are unable to constrain the timing and duration of thermal events. In comparison, low-temperature thermochronology methods, such as apatite fission track thermochronology (AFT), can resolve detailed thermal histories within a temperature range corresponding to oil and gas generation. In the Peel Plateau of the Northwest Territories, Canada, Phanerozoic sedimentary strata exhibit oil-stained outcrops, gas seeps, and bitumen occurrences. Presently, the timing of hydrocarbon maturation events are poorly constrained, as a regional unconformity at the base of Cretaceous foreland basin strata indicates that underlying Devonian source rocks may have undergone a burial and unroofing event prior to the Cretaceous. Published organic thermal maturity values from wells within the study area range from 1.59 and 2.46 %Ro for Devonian strata and 0.54 and 1.83 %Ro within Lower Cretaceous strata. Herein, we have resolved the thermal history of the Peel Plateau through multi-kinetic AFT thermochronology. Three samples from Upper Devonian, Lower Cretaceous and Upper Cretaceous strata have pooled AFT ages of 61.0 ± 5.1 Ma, 59.5 ± 5.2 and 101.6 ± 6.7 Ma, respectively, and corresponding U-Pb ages of 497.4 ± 17.5 Ma (MSWD: 7.4), 353.5 ± 13.5 Ma (MSWD: 3.1) and 261.2 ± 8.5 Ma (MSWD: 5.9). All AFT data fail the χ² test, suggesting AFT ages do not comprise a single statistically significant population, whereas U-Pb ages reflect the pre-depositional history of the samples and are likely from various provenances. Apatite chemistry is known to control the temperature and rates at which fission tracks undergo thermal annealing. The r_mro parameter uses grain specific chemistry to predict apatite’s kinetic behaviour and is used to identify kinetic populations within samples. Grain chemistry was measured via electron microprobe analysis to derive r_mro values and each sample was separated into two kinetic populations that pass the χ² test: a less retentive population with ages ranging from 49.3 ± 9.3 Ma to 36.4 ± 4.7 Ma, and a more retentive population with ages ranging from 157.7 ± 19 Ma to 103.3 ± 11.8 Ma, with r_mr0 benchmarks ranging from 0.79 and 0.82. Thermal history models reveal Devonian strata reached maximum burial temperatures (~165°C-185°C) prior to late Paleozoic to Mesozoic unroofing, and reheated to lower temperatures (~75°C-110°C) in the Late Cretaceous to Paleogene. Both Cretaceous samples record maximum burial temperatures (75°C-95°C) also during the Late Cretaceous to Paleogene. These new data indicate that Devonian source rocks matured prior to deposition of Cretaceous strata and that subsequent burial and heating during the Cretaceous to Paleogene was limited to the low-temperature threshold of the oil window. Integrating multi-kinetic AFT data with traditional methods in petroleum geosciences can help unravel complex thermal histories of sedimentary basins. Applying these methods elsewhere can improve the characterisation of petroleum systems.

How to cite: Spalding, J., Powell, J., Schneider, D., and Fallas, K.: Resolving thermal histories via multi-kinetic apatite fission track data: A case study from Phanerozoic strata within the Peel Plateau NWT, Canada, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3135, https://doi.org/10.5194/egusphere-egu21-3135, 2021.

The southeastern Tibetan Plateau experienced significant tectonic uplift, fault activity, climate change and reorgnization of fluvial systems during the late Cenozoic. All these processes were probably accompanied by rapid rock exhumation. Therefore, rock exhumation history in this region could provide a key to reveal the interaction between tectonics, climate and surface processes. Here, we report new apatite and zircon (U-Th)/He dates from a ~1200 m granite vertical profile, located at Shimian county in the Daliang Mountains, southeastern Tibetan Plateau. The age-elevation relationship and thermal history simulation exhibit a two-phase rock exhumation history, one at ~25 Ma (~1 km/Myr) and a second moderate exhumation from ~15 Ma to present (~ 0.2 km/Myr). This two-phase rapid exhumation history is consistent with that of Longmen Shan and Jiulong in the adjacent areas. For the first phase in Oligocene, abundant geological evidence indicates that it was related to the regional uplift caused by the transpressional deformation during India-Asia convergence. However, there are two distinct explanations for the rapid exhumation from ~15 Ma to present: one group suggested this exhumation was related to the rapid river incision caused by regional uplift; By contrast, based on paleo-altimetry data another group proposed the uplift was ceased before the late Miocene in southeastern Tibetan Plateau, and then the enhanced rainfall caused by the East Asian monsoon resulted in rapid exhumation since the Middle Miocene. Our study suggests that the fast exhumation in southeastern Tibetan Plateau since ~15 Ma cannot be attributed solely to the regional uplift or the intensification of Asian monsoon. Combined with the activity history of the Anninghe fault in the study area and the East Asian monsoon evolution history, we suggest that the regional rock exhumation of southeastern Tibetean Plateau since the Middle Miocene could be the result of the combination of tectonic activity and climate change.

How to cite: Lei, H., Shen, X., Liu, X., Tang, X., and Zhang, S.: Late Cenozoic two-phase rapid exhumation of the Daliang Mountains, Southeastern Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2145, https://doi.org/10.5194/egusphere-egu21-2145, 2021.

Substantial set of recent documentation with sophisticated statistical and analog models have recognized dynamic interchange between subsurface crustal distortion and exogenic erosional processes as the root of geomorphic evolution of Himalaya. Low temperature thermochronology provides insights to enumerate nature and timing of tectonic course from extracted thermal records of vertical moving rock block over geological past. In present study, we used Apatite fission track technique to calculated exhumation rates of Yamuna valley, Garhwal Himalaya. AFT ages of Lesser Himalaya Sequence of Purola region various between 4.0 ±0.8 myr to 9.5±0.6 myr. While AFT ages of LHS along Yamuna River varies form 2.3±0.5 myr to 5.6±0.6 myr and exhumation rates are 2.3-1.2 mm/yr. calculated age of Apatite sample near Main Central Thrust (MCT) is 2.3±0.5 myr which exhumed at the rate of 2.3 mm/yr. Exhumation rates of Purola region are 0.8-1.6 mm/yr.

To link the exhumation rates with present day morphology we used 2 methods; 1) Calculate morphotectonic parameters of Yamuna River valley; 2) compare our AFT ages and exhumation rates with early studies. Drainage pattern in the tectonically active zone is vigorously susceptible to mechanisms such as folding, faulting and basin tilting. Such deformation processes influence the phase of geomorphology, drainage pattern, river incision, elongation, asymmetry, and diversion. Mathematical quantification of drainage morphology elucidate spatio-temporal effect of tectonics. Morphotectonic parameters are stream length gradient index (SL), valley floor height to width ratio (Vf), asymmetry factor (Af), basin shape index (BS) and hypsometric integral (HI) extracted from SRTM DEM with resolution of 30m and are calculated in ArcGIS 10.3. These parameters further integrated to define a single Indaex of relative Active Tectonic (IRAT). Value of IRAT is very high in upper Yamunotri region and low to moderate in Purola region. The exhumation rates are further compared with erosion rates from early studies. Erosion rates derived from ¹⁰Be nuclides (Scherler et al 2014) show very slow erosion rate in Purola region (~ 0.13±0.01 mm/yr) while for Yamunotri region higher erosion rate (>4.9 mm/yr) is recorded. These erosion rates are attributed to subsurface geometry of MCT.

All three approaches together construct an evolution record of study area over geological past.  Exhumation history of Apatite and erosion rates from early studies conclude Yamuna river valley, specifically upper region of valley is very active while Purola region is less active. Morphotectonic parameters harmoniously present similar picture. These combined study point toward relegate control of climate and dominance of ongoing sub-surficial deformation along MCT in Yamuna River valley on geological time scale.

How to cite: Gahlaut, P. and Chandra Patel, R.: Insights of Spatiotemporal evolution of Yamuna Valley, Garhwal Himalaya: Derived from Fission track dating and Morphotectonic analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16290, https://doi.org/10.5194/egusphere-egu21-16290, 2021.

The tropical Northern Andes of Colombia are one the world's most biodiverse places, offering an ideal location for unraveling the linkages between the geodynamic forces that build topography and the evolution of the biota that inhabit it. In this study, we utilize a geomorphic analysis to characterize the topography of the Western and Central Cordilleras of the Northern Andes. We supplement our topographic analysis with erosion rate estimates based on gauged suspended sediment loads and river incision rates from volcanic sequences. In the northern segment of the Central Cordillera, an elevated low-relief surface (2,500m in elevation, ~40x110 km in size) with uniform lithology and surrounded by knickpoints, indicates a recent increase in rock and surface uplift rate. Whereas, the southern segment of the Central Cordillera shows substantially higher local relief and mostly well graded river profiles consistent with longer term uplift stability. These changes in the topography fit with the proposed location of a slab tear and flat slab subduction under the northern Central Cordillera, as well as with a major transition in the channel slope of the Cauca River. We identify several areas of major drainage reorganization, including captures and divide migrations that are supported by our erosion and incision rate estimates. We identify slab flattening as the most likely cause of strong and recent uplift in the Northern Andes leading to ~2 km of surface uplift since 8–4 Ma. Large scale drainage reorganization of major rivers is probably mainly driven by changes in upper plate deformation in relation to development of the flat slab subduction geometry; however, other factors such as climate and emplacement of volcanic rocks likely play secondary roles in this process. Several isolated biologic observations above the area of slab flattening suggest that surface uplift isolated former lowland species on the high elevation plateaus, and drainage reorganization may have driven diversification of aquatic species.

How to cite: Perez-Consuegra, N., Ott, R., Hoke, G. D., Galve, J. P., and Pérez–Peña, J. V.: Topographic response to Neogene variations in slab geometry, climate and drainage reorganization in the Northern Andes of Colombia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9121, https://doi.org/10.5194/egusphere-egu21-9121, 2021.

The landscape at the NE end of the South Island, New Zealand, records oblique plate collision over the last 25 million years. Using low-temperature thermochronology, geomorphic analyses, and cosmogenic ¹⁰Be data, we document the landscape response to tectonics over long (10⁶) and short (10² – 10³) timescales in the Marlborough Fault System (MFS) and related Kaikōura Mountains. Our results indicate two broad stages of landscape evolution that reflect a changing plate boundary through time. In the eastern MFS, Miocene folding above blind thrust faults generated prominent Kaikōura Mountain peaks and formed major transverse rivers early in the plate collision history. By the Pliocene, rotation of the plate boundary led to a transition to dextral strike-slip faulting and widespread uplift that led to cycles of river channel offset, deflection and capture of tributaries draining across active faults, and headward erosion and captures by major transverse rivers within the western MFS. Despite clear evidence of recent rearrangement of the western MFS drainage network, rivers in this region still flow parallel to older faults, rather than along orthogonal traces of younger, active strike-slip faults. Such drainage patterns emphasize the importance of river entrenchment, showing that once rivers establish themselves along a structural grain, their capture or avulsion becomes difficult, even when exposed to new weakening and tectonic strain. Over short timescales (hundreds to thousands of years), apparent catchment-wide average erosion rates derived from ¹⁰Be data show an increase from SW to NE, along strike of the Seaward Kaikōura Range. These rates mirror spatial increases in elevation, slope, channel steepness, and coseismic landslides, demonstrating that both landscape and geochronology patterns are consistent with an increase in rock uplift rate toward a subduction front that is presently locked on its southern end. Remarkably, the form of the topography, hillslopes, and rivers across much of the MFS appears to faithfully record the complex and changing tectonic history of a long-lived, oblique convergent plate boundary.

How to cite: Duvall, A., Upton, P., Collett, C., Harbert, S., Williams, S., Flowers, R., Tucker, G., Stone, J., and LaHusen, S.: Landscape Records 25 Million Years of Tectonic Evolution at an Oblique Convergent Margin, Marlborough Fault System, New Zealand, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3281, https://doi.org/10.5194/egusphere-egu21-3281, 2021.

Rectangular drainage networks are characterized by right-angle channel bends and confluences. The formation of the rectangular pattern is commonly associated with orthogonal sets of fractures, making rectangular drainages an outstanding example of structurally controlled landform evolution. However, the association between geologic structures and rectangular patterns remains circumstantial. So far, no specific mechanisms were suggested to explain the linkage between the emergent right-angle bends and confluences and the preexisting fracture system. This gap is particularly significant for planetary rectangular drainages, where the association with preexisting structures can not be directly observed.

We investigated the mechanistic linkages between geologic structures and the geomorphic drainage pattern in the hyper-arid Ami'az Plain located within the Dead Sea Basin in SE Israel. The Ami'az Plain is incised by a seemingly rectangular canyon system and is also penetrated by hundreds of sub-vertical clastic dikes (mode-I opening cracks infilled with sedimentary material), that reach a width of up to 0.18 m. Additionally, many caves and cavities extend from the banks and heads of the canyon system. Based on field surveys and analysis of a high resolution LiDAR based DEM, we mapped and characterized the Ami’az Plain drainage network and associated geomorphic structures including sinkholes. Our analysis revealed that the canyon system exhibits rectangular characteristics and its tributaries share dominant orientations with the strike of the clastic dikes. Surface and subsurface mapping assisted by Ground scanning LiDAR, together with field experiments, demonstrated that the caves and sinkholes are spatially associated with clastic dikes and that the caves formed by piping erosion along dikes.

Based on these findings, we propose a three-component hydrologic-geomorphic model for the formation of the Ami’az Plain rectangular drainage network: First, clastic dikes act as efficient infiltration pathways for surface runoff into the subsurface, where subsurface flow along clastic dikes induces internal erosion and forms piping caves. Second, collapses of cave roofs create sinkholes. Coalescence of sinkholes and seepage erosion in places where dikes intersect canyon banks and canyon heads generate new tributaries and extend existing ones. Finally, fluvial erosion and bank collapse modify the drainage network. Our observations and model emphasize the critical role of subsurface erosion and the formation of caves and sinkholes in linking fractures to drainage pattern evolution. This linkage could be highly consequential for our understanding of rectangular drainage evolution on planetary and terrestrial surfaces.  

How to cite: Goren, L., Hamawi, M., Mushkin, A., and Levi, T.: Geologic structures control geomorphic patterns: Linking rectangular drainage evolution, underground pipe systems, and clastic dikes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6089, https://doi.org/10.5194/egusphere-egu21-6089, 2021.

Steep and narrow escarpments develop along the eastern margin of the Korean Peninsula. They are compartments of a passive continental margin and thus have been considered tectonically stable. In contrast to the traditional notion, geomorphic markers indicative of the enhanced tectonic uplift since the Late Quaternary (i.e., coastal terraces at several different altitudes) have been observed along the eastern coastal areas of the peninsula. Therefore, the steep escarpments in the eastern margin are assumed to be tectonically reactivated. However, the spatial magnitude and timing of the reactivation and how the escarpments have responded to the reactivation have not been well studied. Knickzone is a typical geomorphic marker, which has long been utilized for deciphering the history and distribution of tectonics. Here, we examined the knickzones of the marginal escarpments, where transient knickzones are likely to be observed, in order to understand the spatial pattern of the Late Quaternary reactivation and its effects on the evolution of the marginal escarpments. We used SRTM 1 arc-second DEMs, satellite images with fine resolution, and geological maps to identify and classify knickzones. We also conducted field surveys for the verification of the identified knickzones. As a result of the knickzone analysis, 46 knickzones were identified in the study catchments. Their mean length and gradient are 461 m and 0.19 m/m, respectively. Most knickzones are at relatively high altitudes (i.e., median elevation 532 m) and thus are placed far from the coast. According to the classification of the identified knickzones, they are formed mainly due to varying rock types (11) or changes in lithologic features of the same rock type (e.g., weathering degree of rocks) (31). Few of them are associated with the accumulation of coarse sediments at a channel junction (3) and meander neck cut-off (1). This result implies that all identified knickzones in the study catchments are stationary rather than transient. Consequently, it postulates that the Late Quaternary tectonic forcing was insufficient to generate any transient knickzone. Otherwise, potential transient knickzones due to the reactivation might have disappeared rapidly during their upstream migration, which seems highly relevant to the high concavity of the stream profiles in the drainage basins of the escarpments. Additionally, the result suggests that transient knickzone is not a good indicator for interpreting the responses of the marginal escarpments to the reactivation during the Late Quaternary.

How to cite: Byun, J.: Missing evidence for landscape transience induced by tectonic forcing since the Late Quaternary in the steep marginal escarpments of the Korean Peninsula, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7384, https://doi.org/10.5194/egusphere-egu21-7384, 2021.

The Kachchh region (NW India), a pericratonic rift basin delimited by E-W trending major thrust faults, is a Low Strain Rate region[PB1] . In this area, the tectonic forcing magnitude is stronger enough to trigger infrequent significant earthquakes but not enough to overprint the climatic forcing signature. As a consequence, the active faults sources of the largest seismic events are largely poorly known and their geomorphic signature is subdued. 

Instrumental and paleoseismological evidence highlights that the eastern part of Kachchh experienced a significant number of seismic events such as the 1819-06-16 Allah Bund earthquake (Mw 7.8, also known as the Rann of Kutch earthquake), the 1956-07-21 Anjar earthquake (Mw 6.1), the 2001-01-26 Bhuj earthquake (Mw 7.6) and the 2006 events (Mw 5.0 and 5.6 earthquake occurred along Island Belt Fault and Gedi fault). 

In this region, the unavailability of useful outcrop information due to a significant climatic overprinting of the fault’s morphological signatures hampers the detection and parametrization of actively deforming faults.

For this reason, in this ongoing work, we propose a multidisciplinary approach, aimed at detecting active geological structures and their related [PB2] surface deformation, which mainly consists of quantitative tectonic geomorphology and paleoseismological analyses and structural interpretation and modelling. Preliminary results are a morphotectonic evolution model and 3D fault model of the study area. Finally, we stress the concept that only a multidisciplinary approach could provide useful information to understand better the highly debated active tectonic framework of the study area.

How to cite: Srivastava, E., Parrino, N., Malik, J., Pepe, F., and Burrato, P.: Looking for the hidden morphological signature of active faults in a Low Strain Rate region: clues from the eastern Kachchh region (NW India), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15982, https://doi.org/10.5194/egusphere-egu21-15982, 2021.

The Baribis-Kendeng Fault System crosscuts the northern part of Java Island (Indonesia). It seems that the fault systems is the continuation westward from the active Flores thrust in the northern offshore of the Lesser Sunda Islands. While the Flores thrust in the east is well documented as an active fault in the back-arc platform (e.g., source of the 2018 Lombok 6.9 Mw earthquake), the nature, timing, and activity of the Baribis-Kendeng Fault Systems, particularly the Baribis Fault Zone (BFZ) in the westernmost part of the system remain elusive. Yet, understanding the geological risk associated with the BFZ is crucial, as it crosscuts densely-populated regions, possibly up to 30 million inhabitants in the megalopolis of Jakarta. Previous studies mostly identified the BFZ by first-order morphotectonic observations, as well as large-scale geodetic and seismotectonic investigations, and assigned historical earthquakes (estimated up to 8.5 Mw in 1780) in northern Java to the BFZ. Ground-truthing the structure and activity of the BFZ from geological arguments is a cornerstone to evaluate associated geohazards.

We first focus on the Cikamurang Ridge, nearly at the eastern part of the BFZ, where uplifted Pliocene-Recent sediment sequences outcrop. Morphotectonic data include an 8-m resolution digital elevation model that we used to map fault lineaments and calculate the channel steepness index of the rivers crossing the mapped fault segments. Field data, including paleoseismological trenching at the central part of Cikamurang Ridge and sediment dating (OSL and radiocarbon) provide temporal constraints on the BFZ activity. Subsurface geophysical data include seismic reflection and resistivity imaging provide better image of the fault geometry in the sub-surface.

Our results suggest that the BFZ has been active in the Cikamurang Ridge during the late-Pleistocene to Holocene times, with deformed sediment sequences dated between 55 and 7 ka. Eastward, the BFZ crosses the Cisanggarung River where the fault deformed ~13-ka old sediments. Westward of the Cikamurang Ridge, both fault lineament interpretation and channel steepness index indicates that the fault continues from Subang regency to Jatiluhur and reaches the area between Jakarta and Bogor. Even though in the area between Jakarta and Bogor the surficial trace of the BFZ is not as clear as the Cikamurang and Subang, the seismic reflection data reveal the blind fault propagation fold. We conclude that the BFZ has a high seismic hazard that requires a careful risk evaluation along its trace, as it threats the numerous infrastructures of the extremely densely-populated West Java.  Comparing to the Flores back-arc thrust, the existence of the BFZ indicate the whole island of Java affected with the back-arc compressive regime as well as the existence of the Kendeng Fault Zone, in the easternmost of the Baribis-Kendeng Fault Systems.

How to cite: Aribowo, S., Husson, L., Natawidjaja, D. H., Authemayou, C., Daryono, M. R., Puji, A. R., Valla, P. G., Pamumpuni, A., Wardhana, D. D., and de Gelder, G.: Active back-arc thrust in North West Java, Indonesia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10469, https://doi.org/10.5194/egusphere-egu21-10469, 2021.

Four M~8 earthquakes in the 20^th century reflect active deformation in western Mongolia as a result of far-field stresses related to the India-Eurasia collision. Historic seismicity indicates that deformation localises around the relatively rigid Hangay dome in central Mongolia, however, tectonic lineaments in the surrounding Valley of Lakes basins suggest more widespread and diffuse deformation. In southern Mongolia, seismicity clusters around the Bogd fault, which ruptured during the 1957 Mw 8.1 Gobi Altai earthquake. To determine whether the kinematics interpreted from this earthquake are regionally representative, especially in consideration of the heterogeneity of intraplate tectonics, we expand the spatial scale of tectonic studies to range between the Gobi Altai and Hangay massifs. We do this by combining observations from regional and local digital elevation models, ground-penetrating radar analyses, geological and geomorphological field data, and seismic reflection data. Additionally, we increase the temporal scale of palaeoseismic studies up until the Middle Pleistocene through OSL and surface exposure dating, to compare the effects of tectonic processes to those of Quaternary climate variations on landscape evolution. We show that reverse and oblique strands of the Bogd fault accommodate <0.3 mm/yr vertical slip rates along the northern margin of the transpressive Gobi Altai massif. Four ~E-W striking faults in the seismically quiescent Valley of Gobi Lakes each have the potential for M~7 earthquakes and they are likely part of a left-lateral strike-slip system rooted at depth. Although cumulatively, the Valley of Gobi Lakes faults are deforming at a regionally representative ~0.3 mm/yr vertical slip rate, recurrence intervals of major earthquakes are much longer than those determined along the Bogd fault (~5-80 ka vs. 3-5 ka). Overall, we interpret the Valley of Gobi Lakes faults to have played a large role in drainage reorganisation and Middle Pleistocene to modern landscape evolution. Sub-surface faults interpreted from seismic reflection data and associated geomorphological irregularities in the Orog Nuur Basin indicate two NW-SE striking lineaments that may connect the Valley of Gobi Lakes fault system to the Bogd fault system. Our observations suggest a more complex and extensive fault system in southern Mongolia than previously expected and the geometry and potential connectivity of faults indicates a continuing northward progression of transpressive deformation from the Gobi Altai towards the Hangay. The obscurity of active deformation in the Valley of Gobi Lakes is likely due to faster erosion and deposition rates and this highlights the importance of understanding the interplay between tectonic, climatic and geomorphological processes and their effects on the landscape system. We suggest that, especially in slowly deforming, intraplate regions, an increase of spatial and temporal scales of active tectonic research is necessary to improve interpretations of tectonically altered landforms, palaeo-environmental reconstructions, and seismic hazard assessments.

How to cite: van der Wal, J. L. N., Nottebaum, V., Stauch, G., Binnie, S. A., Batkhishig, O., Lehmkuhl, F., and Reicherter, K.: Morphotectonic evidence for widespread active faulting in southern Mongolia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13578, https://doi.org/10.5194/egusphere-egu21-13578, 2021.

Low Strain Rate regions (LSRr), i.e., areas deforming at a 1 mm/yr rate or less, represent the most globally widespread areas that host important cities and high-vulnerable anthropogenic assets. The occurrence of infrequent but high-magnitude earthquakes suggests that identifying active structures in the LSRr is one of the primary challenges for both the scientific community and modern societies.

In such regions, one of the main issues in identifying active faults is the lack of useful outcrop data due to the anthropogenic and climate overprinting of the faults morphological signature. In this work, we propose a multidisciplinary approach designed to detect active geological structures and their related deformation. To test this approach, we selected as a natural laboratory an LSRr located between two major cities of Sicily (southern Italy).  This area lies into the northern sector of the Apennine-Maghrebian fold and thrust belt and its offshore prolongation.

Our approach consists of quantitative morphotectonic, offshore and onshore tectonostratigraphic and GNSS joint analyses. The main achieved results are 1) the first evidence of active, shallow-sited, NNW-trending transpressive blind faults that extends partially offshore for about 30 km, which décollement levels located at about 3 and 1 km depth, respectively and their 3D model, 2) a morphotectonic evolution model, that represents where and how these geologic structures drove the landscape evolution of the study area. Finally, we highlight that only a multidisciplinary approach could be useful for detecting and parametrising active faults in slow deforming areas that cross the coastline physical limit.

How to cite: Parrino, N., Pepe, F., Burrato, P., Dardanelli, G., Di Maggio, C., Corradino, M., and Pipitone, C.: Elusive active faults in a low strain rate region (Sicily, Italy): hints from a multidisciplinary land-to-sea approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15425, https://doi.org/10.5194/egusphere-egu21-15425, 2021.

The feedback between climate driven processes; weathering, erosion, sediment transport, and deposition, and extensional tectonics is limited to a few studies (Burov and Cloething, 1997; Burov and Poliakov, 2001; Bialas and Buck, 2009; Theunissen and Huismans, 2019; Andrés-Martínez et al., 2019) despite these processes having been shown to impact the stress state and deformation along active orogens (Koons, 1989; Molnar and England, 1990; Avouac and Burov, 1996; Willett, 1999). Here we utilize a fully coupled landscape evolution and thermomechanical extensional model to investigate the potential impact on faulting and extension due to lake loading changes driven by changes in climate on processional timescales. Fault analyses focusing on heave, throw, and magnitude of dip on faults generated within each model are used to characterize individual faults response to stress changes and rift basin evolution. Preliminary results indicate that fluctuations in lake levels in response to climate change may impact the lithospheric stress state by changing both fault and basin geometries within an extensional basin.

How to cite: Allen Langhans, A., Moucha, R., and Paciga, M. K.: Fluctuating Lake Levels in Rift Basins and its Impact on Extensional Tectonics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10283, https://doi.org/10.5194/egusphere-egu21-10283, 2021.

In active foreland basins, stratigraphic unconformities develop on the flanks and crests of the uplifting thrust-related structures and correspond to correlative conformities in the adjacent depocenters. The geometrical, morphological, stratigraphic, sedimentological, and petrographic attributes of unconformities and associated sediments are highly variable from the uplifting to the subsiding basin sectors. In Quaternary continental foreland basins, landscape evolution, sedimentation, and the nature of the geological boundaries are controlled by the competing turnovers of climate (i.e. glacial advances and retreats) and tectonics (i.e. steady-state uplift/subsidence vs. unsteady deformation increments).

In order to recognize the fingerprints of tectonic and climatic factors on the nature of the stratigraphic unconformities, we studied the Pleistocene shallow marine (Calabrian) to alluvial and glacio-fluvial sediments (Calabrian-Latest Pleistocene) associated to the active external arc of the N-Apennine thrusts in the Quaternary Po basin of Lombardy (N-Italy).

A set of intra-basin reliefs corresponding to ramp-folds was the key-site to describe the nature and attributes of the exposed Pleistocene unconformities and stratigraphy. We integrated different-scale geological, sedimentological, stratigraphic, geo-pedological, geomorphological, and structural field surveys, constrained by C14 and OSL age determinations, to down-trace the stratigraphic boundaries to the subsurface and to assist correlation of borehole logs and geophysical images. The surface facies associations of the stratigraphic units were compared to the litho-textural associations of their subsurface equivalents to draw the best fitting surface-subsurface model, which was constrained to the geological evolution and chronostratigraphy. A hierarchic 3D geological model was computed by the potential field method, which includes the 4D attributes of the stratigraphic boundaries and unconformities organized into three hierarchic orders. Among them, five Quaternary high-rank, and seven intermediate-rank unconformities were recognized.

The high-rank unconformities (Gelasian, intra-Calabrian, Early-Middle Pleistocene, Late Pleistocene and Latest Pleistocene-Holocene unconformities) are erosional, angular (high angle), composite, diachronous surfaces. They originated in front of and above the uplifting ramp-folds, where the discrete, polyphase, and unsteady propagation stages of the blind outermost Apennines arc directly controlled sedimentation, erosion, and accommodation patterns. The intermediate- and low-rank stratigraphic boundaries are either: (i) stratigraphic surfaces of erosion and deposition, occasionally with low-angle unconformity; (ii) stratigraphic surfaces of aggradation (covered by late Pleistocene loess units at places); (iii) morphological surfaces of stabilization marked by (paleo-) soils. These attributes and the 3D relations with the high-rank unconformities show that these surfaces formed during steady uplift/subsidence increments and/or at times or sites of tectonic quiescence. In these cases, the development of erosion surfaces, facies and provenance changes are not associated to tectonic-induced angles, wedging or fanning of sedimentary units. Chronological constraints link these changes to the regional advances and retreats of the Pleistocene alpine glaciers, suggesting that the intermediate-rank surfaces are mostly dependent on the major climate changes, while the low-rank ones relate to depositional unsteadiness, either autocyclic or short-term allocyclic. 

How to cite: Zuffetti, C. and Bersezio, R.: Active thrusting and glacial controls recorded by stratigraphic unconformities in a Quaternary foreland basin (Po basin, Northern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9250, https://doi.org/10.5194/egusphere-egu21-9250, 2021.

River terraces provide insight into the spatial-temporal patterns of transient tectonic and climatic forcings. The Tropoja Basin is located at the junction of the Dinaride-Albanide-Hellenide belt in north-eastern Albania and is part of the hanging wall of the Shkoder Peja Normal Fault (SPNF) system, which accommodated orogen-parallel extension since Early- to Mid-Miocene times. The basin features Plio-Pleistocene fill comprising lacustrine deposits (Pliocene) overlain by sub-horizontal layers of carbonate-rich conglomerates and marl that are interlayered by reddish clay. We found that this fill was incised by at least three generations of river terraces (T1-T3). The controls on river terrace formation within the area, i.e. faulting, climate events and drainage evolution, have been unclear so far. In this study, we date the river terraces within the Tropoja Basin with ³⁶Cl-cosmogenic-nuclide depth-profiles dating and combine these results with further fluvial geomorphic analysis of digital elevation models (DEM) to assess the process of terrace formation in the light of region-wide drainage basin reorganization.

³⁶Cl-depth-profiles dating yield ages of ~ 8.8 ka for the youngest terrace (T1) and ~ 15.4 ka for the intermediate terrace level (T2), indicating that both terraces formed after the Last Glacial Maximum (LGM). Imbrication of conglomeratic clasts in terrace T2 suggests that the paleo flow was southwest directed at the time of deposition followed by a high incision rate of ~7 mm/yr. Also, we checked for activity of the SPNF and its potential impact on terrace formation in the basin by calculating normalised channel steepness index (K_sn) for streams crossing the fault. We found that K_sn-values do not change across that part of SPNF, thus indicating inactivity of the fault in the late Pleistocene to Holocene times. Instead, Ksn-values correlate well with the upper limit of the ice sheet of the LGM of the Valbona Valley. Despite the recent inactivity of the SPNF, the fault might have controlled the spatial fluvial bedrock competence by emplacing carbonates in the footwall adjacent to ophiolites and mélange in the hanging wall forming the floor of the Tropoja Basin. Chi-values of the regional river network in the Tropoja Basin (includes the Valbona and Gashit Rivers, parts of the Drin River system) reveals that the basin was internally drained.

We conclude that the Pleistocene fill of the Tropoje Basin post-dates most, if not all normal faulting. The time difference between Mio-Pliocene normal faulting and Pleistocene filling of the basin suggests that sedimentation and incision were controlled directly by climate and basin connectivity through the river network to the regional base-level of the Adriatic Sea. Internally drained, the basin led to lake formation prior the LGM where at times reconnected with regional base-level of the Adriatic Sea after via the Drin River system. This transient evolution of the river network was characterised by basin filling and potential river over-spilling leading to drainage integration events with increased headward erosion and river entrenchment. 

How to cite: Gemignani, L., Mittelbach, B., Simon, D., Hippe, K., Grund, M., Rohrmann, A., and Handy, M.: Pleistocene to Holocene river terraces in the Tropoja Basin (northeastern Albania) record tectonic and climatic fluctuations modulated by drainage integration processes., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10781, https://doi.org/10.5194/egusphere-egu21-10781, 2021.

Quaternary sea-level curves provide crucial insights to constrain tectonic and climatic processes, but require calibration with geological constraints that are particularly scarce for cold periods prior to the last glacial-interglacial cycle. To derive such constraints, we re-visit the Huon Peninsula in Papua New Guinea, which is a classic coral reef terrace (CRT) site that was used for the earliest relative sea-level (RSL) curves. We use digital surface models calculated from 0.5m Pleiades satellite imagery to improve RSL constraints, and unlike previous studies, we find that large-scale tilting of the terrace sequence is generally N-directed. This implies that RSL estimates are several meters higher than previously thought for most highstands over the past ~125 ka. We use the large-scale geometry of the terrace sequence to estimate sea-level highstands up to ~400 ka, and our results suggest that global mean sea-level curves derived from oxygen isotopes consistently underestimate sea-level during the relatively cold Marine Isotope Stages 3, 5a, 5c, 6, 9a and 11a, up to ~10-20 m. We use coral reef models to show that our age interpretation is consistent with the overall terrace sequence morphology, and fits between models and topography improve when adjusting sea-level highstands according to our findings.

How to cite: de Gelder, G., Husson, L., Pastier, A.-M., Chauveau, D., Fernández-Blanco, D., Pico, T., Authemayou, C., and Pedoja, K.: High-resolution topography of the uplifting Huon Peninsula (Papua New Guinea) reveals high interstadial sea-levels over the past ~400 ka, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15164, https://doi.org/10.5194/egusphere-egu21-15164, 2021.

Denudation of carbonate terrains occurs by the contribution of both chemical and mechanical weathering. In-situ cosmogenic ³⁶Cl is a robust proxy to quantify the long-term total denudation rate of carbonate rocks. In this study, we defined the steady-state denudation rate of carbonate bedrock using ³⁶Cl for 10⁵-10⁶ years under the temperate Mediterranean to semi-arid climate in and around the Taurus Mountain Range, S-SW Turkey. We collected 13 samples from different lithological units; Jurassic-Cretaceous neritic limestone in the temperate western Taurus, Miocene neritic limestone in the semi-arid Central Taurus, and Mesozoic marbles in the continental part of Central Taurus. The calculated denudation rates range from 28.9 ± 1.4 mm/ka in the Mediterranean coastal range to 1.6 ± 0.1 mm/ka towards northern continental/rain shadow. We compared the denudation rates with a range of parameters such as topographic, climatic, lithologic and mechanical properties of rocks. For almost all samples denudation rate increases with elevation, with two exceptions with the highest rates despite their lower elevations. This high denudation rates could be due to their proximity to the sea. Our results showed that denudation rates decrease with increasing distance from the coast. All denudation rates showed a positive correlation with mean annual precipitation (MAP ~ 400-760 mm) as suggested by other studies worldwide. Annual temperatures (MAT ~ 6-16 °C), however, has a negative correlation with the denudation rates, i.e. the highest denudations occur in the low temperatures (MAT ~ 6-8 °C). The mechanical strength of the rocks was measured with a Schmidt hammer in the field. The high rebound values of Schmidt hammer, indicating the high mechanical strength, correlate with low denudation rates. Nevertheless, the mechanical strength of the carbonate bedrock is not as effective as precipitation or available moisture on denudation rates. This could be shown by two samples close to the Mediterranean which both have high mechanical strength nonetheless show the highest denudation rates. In conclusion, our study suggests that carbonate bedrock denudation in Taurus Mountain correlates with high elevation (~ 1900-2250 m), high precipitation (~ 700-800 mm), low temperatures (~ 6-8 °C) and short distances from the Mediterranean coast.

How to cite: Hashemi, K., Sarıkaya, M. A., and Wilcken, K. M.: Defining denudation rate of carbonate rocks using cosmogenic 36Cl in the Taurus Mountain, S-SW Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2915, https://doi.org/10.5194/egusphere-egu21-2915, 2021.

The Tatra mountains, the northernmost portion of the Central Western Carpathians, host a stunning alpine landscape despite an average elevation that rises 1.4 km above the surrounding lowlands. Regional geomorphology studies on both sides of the range correlate various landforms interpreted to be glacial in origin with all each of the eight major Alpine glacial  events based largely landscape position, and in some cases geochronologic constraints. This regional relative chronology assumes that wet-based mountain glaciers are efficient agents of erosion and each successive glaciation lowered the valleys within the Tatra. While the tendency of subsequent glaciations to obscure evidence of previous events makes it difficult to study the work done by past glacial episodes, the cave networks on the northern side of the Tatra offer a way to evaluate the amount and timing of valley lowering with U-series dating of speleothems. Epiphreatic and paleophreatic caves that developed near the water table and dried out as valley deepening occurred can serve as excellent recorders of the valley incision history.

Speleothems were collected from a number of cave levels present throughout the northern Tatra, of which only a subset were suitable for U-series geochronology. The oldest speleothems collected in active epiphreatic passages on the valley bottom level from each valley are consistently between 284-325 ka (MIS 8-9). This shows that the modern karst drainage system of the Tatra was established prior to the late Middle Pleistocene, and the cave conduits changed to epiphreatic or vadose conditions between 280 and 330 ka. Since the lowest cave level is at or below the modern valley floor, we can conclude that no valley incision occurred after ~330 ka, which includes both the penultimate and last glaciations periods. Clearly, the regional glacial chronologies in the Tatra must be reassessed. The implications of our findings demonstrate that the assumption of successive valley lowering should not be assumed and that even the extensive MIS2 glaciation did not result in valley lowering despite its size.

How to cite: Szczygieł, J., Hercman, H., Hoke, G., Gąsiorowski, M., Błaszczyk, M., and Sobczyk, A.: Not every large glacial episode lowers valley bottoms: inisghts from the cave systems of the Tatra Mts (the Western Carpathians), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9389, https://doi.org/10.5194/egusphere-egu21-9389, 2021.

The basal thermal regime of glaciers is a first-order control on the spatial patterns of glacial erosion. Polythermal glaciers contain both cold-based portions that protect bedrock from erosion and warm-based portions that actively erode bedrock. Climatic controls on the thermal structures of mountain glaciers and the spatial patterns of glacial erosion has received little study. In this study, we aim to fill this gap by modeling the impact of various climatic conditions on glacier basal thermal regimes and patterns of glacial erosion in mountainous regions. We couple a sliding-dependent glacial erosion model with the Parallel Ice Sheet Model (PISM) to simulate the evolution of the glacier basal thermal regime and glacial erosion in a synthetic landscape. We find that glacial erosion patterns follow the patterns of the basal thermal regime. Cold temperature leads to limited glacial erosion at high elevations due to cold-based conditions. Increasing precipitation could overcome the impact of cold temperature on the basal thermal regime by accumulating thick ice and lowering the melting point of ice at the base of glaciers. High precipitation rates, therefore, tend to cause warm-based conditions at high elevations, resulting in intensive erosion near the peak of the mountain range. Previous studies often assess the impact of climate on the spatial patterns of glacial erosion by integrating climatic conditions into the equilibrium line altitudes (ELAs) of glaciers, and glacial erosion is suggested to be maximal around the ELAs. However, our results show that different climatic conditions could produce glaciers with similar ELAs but different patterns of basal thermal regime and glacial erosion, suggesting that there might not be any direct correlation between ELAs and glacial erosion patterns.

How to cite: Lai, J. and Anders, A.: Climatic controls on mountain glacier basal thermal regimes dictate spatial patterns of glacial erosion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3702, https://doi.org/10.5194/egusphere-egu21-3702, 2021.

Rock fracturing induced by tectonic deformation is thought to promote faster denudation in more highly fractured areas by lowering grain size and directing the flow of water. That the density and pattern of fractures in a landscape play a role in controlling erosion and landscape evolution has been known for over a century, but not until recently do we have tools, like cosmogenic nuclides, to quantify erosion rates in places with varying fracture densities. In the Nahuelbuta Range in south-central Chile, we observed that >30-m thick regolith exists next to patches of unweathered bedrock. We hypothesize that the density of fractures dictates the pace and patterns of chemical weathering, regolith conversion, and erosion in the Nahuelbuta Range. To test this, we used in situ cosmogenic ¹⁰Be to obtain denudation rates from amalgamated samples of bedrock, corestones and soils, and measured fracture density and orientation, as well as hillslope boulder size in several sites in the Nahuelbuta Range. We found that more highly fractured areas indeed have higher denudation rates than less fractured areas, and that bedrock denudation rates are ~10 m/Myr while soil denudation rates are ~30 m/Myr, suggesting that soil-covered areas may be sites of higher fracture density at depth. Fractures have orientations that match mapped faults across the Nahuelbuta range, and thus are considered to be tectonically-induced. In addition, both fracture and fault orientations match the orientation of streams incising the range, suggesting that fractures control stream channel orientation by weakening bedrock and thus directing flow.

How to cite: Lodes, E., Scherler, D., Wittmann, H., and Van Dongen, R.: Patchy bedrock explained: Tectonic fracture control on landscape evolution patterns in south-Central Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9231, https://doi.org/10.5194/egusphere-egu21-9231, 2021.

Subsurface fracturing and weathering in bedrock are typically studied and imaged with conventional remote geophysical techniques. We introduce a new technique, muography, for carrying out such studies. This technique is based on the detection of atmospheric cosmic-ray induced muon particles after they pass through rock. The method plots the attenuation of muon flux in materials of different thickness and density (simply, dense materials “stop” more muons). The raw muon flux is translated into 2D images and 3D models showing variations in mean densities in a visually meaningful manner. As a rule of thumb, a 1% density difference between two rock bodies yields approximately 3% difference in the respective muon fluxes. The muographic density maps cover the Volume of Interest (VOI) that is located between the muon detector(s) and the source of muons (sky). Hence, the detector must be installed behind the VOI. Appropriate settings for muography include the sides of mountains, hills, cliffs and gorges, and in tunnels or boreholes below the ground surface.

Muography provides an interesting new opportunity to study and remotely image subsurface fracturing and weathering. Understanding fracturing and weathering is important as they control, for example, erosion, soil formation, the stability of rock and soil slopes, and stability of tunnels. Weathering also has a link to past climates, palaeogeographic reconstructions, and natural geochemical cycles. Weathered bedrock is also a target for mineral exploration. Due to these reasons, we are planning field surveys in northern Finland. These surveys are also used for fine-tuning the muon detector’s operational parameters and to improve its current design to cope with operating conditions in the Arctic. The survey area around Vuotso lies within the ice-divide zone of the Fennoscandian ice sheet, a zone of low glacial erosion through the Pleistocene. We have identified two survey targets: (i) a tor-studded granite dome at Riestovaara, with extensive granite outcrops that show curved sheet joints and (ii) Mäkärä, a rare-earth mineral prospect in the Tana Belt where amphibolites and garnet–biotite gneisses are covered by thick kaolinitic saprolites of pre-Pleistocene age and overlain by clay-rich till enriched in La and Y. Reconnaissance muon surveys across these contrasting terrains can be calibrated against a wealth of existing GTK data from field mapping and boreholes. The muon survey aims to provide important new subsurface information on fracture patterns at depth on the Riestovaara dome and on deep weathering patterns at Mäkärä. Muography has potential to become a fundamental tool for low-cost subsurface surveying, with applications in geomorphology, mineral exploration, and civil and mining engineering.

How to cite: Holma, M., Sarala, P., Hall, A. M., Kuusiniemi, P., Tanaka, H. K. M., and Varga, D.: Studying bedrock fracture and weathering patterns with cosmic-ray induced muon particles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9886, https://doi.org/10.5194/egusphere-egu21-9886, 2021.

Molybdenum (Mo) isotopes are known as sensitive recorders for changes in redox conditions because the oxidized form of Mo (Mo VI) is more soluble, whereas its reduced form is more particle reactive. Previous studies suggest that Mo isotopic fractionation during the weathering process is controlled by atmospheric input, Mo host, and bedrock composition. However, Mo isotopic variation and processes influencing fractionation in weathering profiles overlying ultramafic bedrock, the early Earth analog, have yet to be explored. This study explores for the first time (1) Mo behavior and (2) isotopic fractionation in two representative and intensely-weathered lateritic profiles overlying ultramafic bedrock of the East Sulawesi Ophiolite, Indonesia. Mo concentrations measured on samples obtained from laterite successions studied here range between 60 - 537 ppb and are overall higher compared to bedrock values ranging between 9 - 45 ppb. The Mo isotope compositions of laterite samples vary between -0.043‰ to -0.161‰ δ⁹⁸Mo_NIST3134. The overall close to mantle Mo isotopic composition of the laterite samples, their small Mo isotope variability, and the covariation between Mo and Ti concentrations suggest low mobility of Mo during chemical weathering and laterite formation. This low Mo mobility is likely a consequence of a) the low Mo concentration of the ultramafic protolith and b) adsorption of Mo to secondary Fe-Oxides during laterite formation under oxic weathering conditions.

How to cite: Damanik, A., Wille, M., Grosjean, M., Cahyarini, S. Y., and Vogel, H.: Mo mobility in lateritic weathering profiles overlying ultramafic rocks of the East Sulawesi Ophiolite, Indonesia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1235, https://doi.org/10.5194/egusphere-egu21-1235, 2021.

Long-term cooling, pCO₂ decline, and the establishment of permanent, polar ice sheets in the Neogenehas frequently been attributed to increased uplift and erosion of mountains and consequent increases in silicate weathering, which removes atmospheric CO₂. However, an increasing weathering flux is incompatible with a balanced atmospheric CO₂budget [1]. For example, a weathering increase scaled to frequently invoked erosional increase [2] would have removed nearly all carbon from the atmosphere. Further, the marine ¹⁰Be/⁹Be proxy indicates constant silicate weathering fluxes over the past 10 Ma [3].

Rather, as volcanic CO₂ emissions have been largely constant yet atmospheric CO₂ decreased, as indicated by the marine ¹¹B/¹⁰B proxy, an increase in “land surface reactivity” has likely driven global cooling [4]. Land surface reactivity quantifies the likelihood of weathering zone material to react with carbon derived from atmospheric CO₂ and represents the degree of coupling between weathering and climate. That surface reactivity has increased during the Neogene is confirmed by the stable ⁷Li/⁶Li seawater proxy, which increases during the Neogene. The question we now need to address is thus: what has caused the increase in land surface reactivity? What is needed is an increased availability of Ca and Mg-rich primary minerals in the global critical zone. This could have come about by 1) an increased exposure of mafic volcanic rock; 2) supply of fresh glacial debris; 3) widespread rejuvenation of the continental land surface by faulting; 4) more efficient mineral dissolution by biota; or 5) an increase in erosion rate with or without mountain uplift. Only explanation 1) can be discounted as this hypothesis fails to satisfy the marine Sr and Os radiogenic isotope records. Explanations 2 – 5 remain. In all of these the role of erosion is to remove weathered material. Indeed, parsimonious geochemical models are roughly compatible with a doubling in global erosional mass flux since 10 Ma [1].

(1) Caves Rugenstein, J.K., D.E. Ibarra, and F. von Blanckenburg, Neogene cooling driven by land surface reactivity rather than increased weathering fluxes. Nature, 2019.

(2) Molnar, P., Late Cenozoic increase in accumulation rates of terrestrial sediment: how might climate change have affected erosion rates? Ann. Rev. Earth Planet. Sc., 2004.

(3) Willenbring, J.K. and F. von Blanckenburg, Long-term stability of global erosion rates and weathering during late-Cenozoic cooling. Nature, 2010.

(4) Kump, L.R. and M.A. Arthur, Global chemical erosion during the Cenozoic: Weatherability balances the budgets, in Tectonic Uplift and Climate Change. 1997.

How to cite: von Blanckenburg, F., Caves-Rugenstein, J. K., and Ibarra, D. E.: Increased land surface reactivity as the driver of Neogene cooling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14888, https://doi.org/10.5194/egusphere-egu21-14888, 2021.

Anthropogenic global warming over the last century has led to a steady increase of CO₂ in the atmosphere. One of the consequences of increasing CO₂ concentrations is ocean acidification, a phenomenon problematic to marine biodiversity and biogeochemistry. The ocean reservoir takes up 25% of CO₂ from the atmosphere both chemically and biologically. This potential can be made use of to promote CO₂ uptake from the atmosphere while mitigating ocean acidification and protecting biodiversity using negative emission technologies associated with the ocean. We have investigated the potential of various alkaline minerals to stabilize seawater pH overtime on a small scale. Those alkaline minerals were predicted to be appropriate for ocean alkalinity enhancement and can offer a toolset to mitigate CO₂ from the atmosphere. Specifically, we have examined how chalk, calcite, dolomite, limestone, and olivine affects seawater pH and total alkalinity (TA) on timescales of several months. Thereby, we could identify two promising minerals, dolomite and olivine, and develop a strategy for mineral additions to buffer the seawater pH. Importantly, the often proposed had an unexpected opposite impact and massively lowered the seawater pH over a timescale of 100 days. The identified advantageous minerals will inform our experiments on primary producer cultures and natural consortia.

How to cite: Rønning, J. and Löscher, C.: Ocean alkalinity enhancement as a tool to mitigate ocean acidification and facilitate CO2 uptake from the atmosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2264, https://doi.org/10.5194/egusphere-egu21-2264, 2021.